pw_ide: Remove Path.with_stem() uses
pw_ide: Remove Path.with_stem() uses

Path.with_stem() was added in Python 3.9, and we're trying to support
Python 3.8.

Change-Id: Ic1a416f238f3445e38bb2c2a2c750ba41e3b8843
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/111075
Reviewed-by: Chad Norvell <f2b1b54074a2cea3f685a7cf4fc055999c2f0cd6@google.com>
Pigweed-Auto-Submit: Rob Mohr <d07614a8a0b466db08f68224f87d738b0f9615cf@google.com>
Commit-Queue: Rob Mohr <d07614a8a0b466db08f68224f87d738b0f9615cf@google.com>

google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed